Theory Of Operation-Can Bus Faults
WARNING: This page is about a different car, the 2024 RAM ProMaster EV. However, it is still accessible from the selected car via links, so may be relevant.
Types of diagnostic communication on a vehicle:
- Scan tool to the Security Gateway (SGW) Module
- ECU to ECU
- ECU to Device
- Device to ECU
| CAN BUS FAULT TYPES | |
|---|---|
| LOSS OF COMMUNICATION | Set by an active receiving/reporting ECU that does not detect communication from another ECU that is connected to the same CAN Bus network. Insufficient power, ground, bus voltage, or inaccurate vehicle configuration will cause a loss of communication. |
| IMPLAUSIBLE MESSAGE | Set by an active receiving/reporting ECU that determines the CAN Bus network data from the transmitting/offending ECU is missing part of the message, or the message is an irrational value. |
| MISSING MESSAGE | Set by an active receiving/reporting ECU that determines the CAN Bus network data message is missing partial information when sent from the active transmitting/offending ECU. |
| BUS OFF | Set by an ECU that has experienced approximately 32 transmit errors. This may be due to ECU internal faults as well as external bus faults, such as a shorted circuit or when connecting and disconnecting testing tools to the diagnostic connector. |
| PHYSICAL | Only detected by ECUs equipped with a transceiver that is able to detect shorted bus circuits. ECUs not equipped with this detection may instead set bus off faults, due to shorted bus circuit(s). |
For additional information on the CAN Bus networks, Refer to COMMUNICATION, DESCRIPTION AND OPERATION .